The presently disclosed subject matter relates to an electrocardiogram measuring apparatus and a synthesized electrocardiogram generating method.
In the case where a standard 12-lead electrocardiogram is acquired from the patient, ten electrodes connected to an electrocardiograph functioning as an electrocardiogram measuring apparatus are used, and attached to six places for measuring chest leads, and four places for measuring limb leads, respectively. Based on cardiac potentials detected from the ten electrodes, then, the electrocardiograph calculates and outputs six limb lead waveforms (I, II, III, aVR, aVL, and aVF) of standard 12 leads, and six chest lead waveforms (V1, V2, V3, V4, V5, and V6) of standard 12 leads.
Usually, relationships between lead waveforms for obtaining a standard 12-lead electrocardiogram and cardiac potentials in measurement portions are as follows:
lead I: vL−vR
lead II: vF−vR
lead III: vF−vL
lead aVR: vR−(vL+vF)/2
lead aVL: vL−(vR+vF)/2
lead aVF: vF−(vL+vR)/2
lead V1: v1−(vR+vL+vF)/3
lead V2: v2−(vR+vL+vF)/3
lead V3: v3−(vR+vL+vF)/3
lead V4: v4−(vR+vL+vF)/3
lead V5: v5−(vR+vL+vF)/3
lead V6: v6−(vR+vL+vF)/3
where v represents a potential which is detected in each of the electrode attachment positions.
Diagnosis which is to be performed on a heart disease of the patient by using such many electrodes is enabled in a state where the patient is kept quiet, only in a large fully equipped hospital or the like.
However, in the case where home care or emergency medicine is performed, for example, it is often difficult, from the viewpoint of the condition of the patient, to use many electrodes and attach the electrodes to adequate positions of the body surface of the living body. Moreover, there is a case where a multi-channel signal for obtaining many lead waveforms is hardly transmitted. In such a case, usually, the number of channels through which signals for an electrocardiogram can be transmitted is about one or two (one or two leads). Diagnosis of a heart disease is performed by using two to four electrodes at most and measuring several lead waveforms of standard 12-lead waveforms.
Concerning this, there are a method of constructing a synthesized 12-lead electrocardiogram, and an electrocardiogram inspection apparatus in which a standard 12-lead electrocardiogram that enables diagnosis and treatment of various heart diseases to be properly performed is reconstructed by a subset of a lead system having a minimum number of leads required for obtaining a standard 12-lead electrocardiogram (see Japanese Patent No. 4,587,008).
In the method of constructing a synthesized 12-lead electrocardiogram which is disclosed in Japanese Patent No. 4,587,008, leads I and II which are limb leads in the case where a standard 12-lead electrocardiogram is to be obtained, and leads V1 and V5 or V6 which are two of chest leads are used as a subset of a lead system consisting of a minimum number of channels. These leads enable leads III and aV (leads aVR, aVL, and aVF) to be obtained by calculation based on the above-described inherent relationships of the leads. The remaining ones of the chest leads, or leads V2, V3, V4, and V6 or V5 are synthesized by calculation using conversion coefficients (derivation matrix) which are produced in consideration of relationships between potential-lead vectors and cardiac vectors.
In a synthesized 12-lead electrocardiogram which is obtained as described above from inherent relationships of leads and produced conversion coefficients, a subset of a lead system for a related-art standard 12-lead electrocardiogram is used, and, in attachment of electrodes, therefore positioning to predetermined portions can be performed easily and surely. Consequently, the attachment work does not require a lot of skill. Moreover, an accurate standard 12-lead electrocardiogram can be reconstructed, and therefore various heart diseases can be diagnosed and treated properly.
In a related-art electrocardiograph, therefore, an abnormality of electrocardiogram waveforms can be checked and diagnosed not only in the case where a standard 12-lead electrocardiogram is obtained from six limb leads and six chest leads by using ten electrodes, but also in the case where an accurate synthesized 12-lead electrocardiogram is synthesized by using the method disclosed in Japanese Patent No. 4,587,008.
Another case where a synthesized electrocardiogram related to an application of standard 12 leads is necessary will be described. In the above-described standard 12-lead electrocardiogram, when it is applied to diagnosis of myocardial infarction, it is easy to check and diagnose an abnormality of electrocardiogram waveforms with respect to the anterior/lateral wall in which blockage of the coronary arteries supplying the blood flow to the cardiac muscle may occur. With respect to the posterior or right posterior wall, however, the sensitivity is low because positions of electrodes are remote from the heart. According to a research paper, ST elevations of many posterior acute myocardial infarctions (AMIs) appear in V7, V8, and V9. In a standard 12-lead electrocardiogram, therefore, ST elevations are often overlooked. It has been proposed that, if necessary, the above-described additional leads are measured. In the case where a standard electrocardiograph is used, however, the measurement must be conducted two times, and particularly V7, V8, and V9 are on the back side and therefore hardly measured. Therefore, an electrocardiograph having an additional lead function and a method of deriving an additional-lead electrocardiogram have been proposed in which, by using measurement signals of a standard 12-lead electrocardiogram, electrocardiogram waveforms of V7, V8, and V9 are synthesized for diagnosis of inferior wall infarction, and those of V3R, V4R, and V5R are synthesized for diagnosis of right ventricular infarction, whereby accurate diagnosis information can be provided (see Japanese Patent No. 4,153,950).
In the technique disclosed in Japanese Patent No. 4,153,950, however, electrocardiogram waveforms of portions to which an electrode is not attached, i.e., waveforms of synthesized electrocardiograms are calculated by using conversion coefficients indicating relationships between measured lead vectors (lead vectors of portions to which an electrode is attached) and synthesized lead vectors (lead vectors of portions to which an electrode is not attached), and hence the accuracy of the conversion coefficients affects synthesized electrocardiograms of the subject, and the accuracy of diagnosis of a heart disease. As a conversion coefficient, usually, the average value (hereinafter, referred to as the population coefficient) of a plurality of conversion coefficients which are obtained from a large unspecified number of persons. A population coefficient can statistically assure a certain kind of conversion accuracy, but is hardly regarded as an optimum conversion coefficient for the subject himself/herself. Therefore, the difference between a synthesized electrocardiogram and “true values” (values which would be obtained if measured) cannot be sometimes satisfied from a clinical viewpoint.
In view of the circumstances, a synthesized electrocardiogram generating system has been proposed in which a conversion coefficient (hereinafter, referred to as the personal coefficient) of the subject himself/herself is previously stored in a database according to the type of a synthesized electrocardiogram, and the conversion coefficient is read out as required, whereby a synthesized electrocardiogram can be acquired (for example, see JP-A-2012-029904).
In the synthesized electrocardiogram generating system of JP-A-2012-029904, in order to calculate personal coefficients for deriving desired leads, however, leads of arbitrary portions of the subject himself/herself must be previously measured, and therefore there is a problem in that the system is cumbersome and burdensome.